Catalytic dewaxing is now a part of many processes for production of desired hydrocarbon products from basestocks having an appropriate boiling range. Catalytic dewaxing allows for conversion of less desirable molecules within a basestock into molecules with more favorable properties for a particular application. Catalytic dewaxing can be used to improve the properties of basestocks in order to form lubricating oils. Catalytic dewaxing also has applications in other areas, such as improvement of cold flow properties of diesel fuels.
Catalytic dewaxing can occur by either cracking of feedstock molecules or by isomerization of feedstock molecules. Catalysts which perform dewaxing primarily by cracking tend to produce products with lower viscosity index and also tend to have lower yields than catalysts which perform dewaxing primarily by isomerization. As a result, isomerization dewaxing catalysts are preferred in many applications.
Conventional isomerization dewaxing catalysts, however, are susceptible to poisoning by sulfur and nitrogen contaminants in a feedstock. As a result, a hydrotreating step or other pre-treatment step often precedes a catalytic dewaxing step, in order to reduce the sulfur and/or nitrogen in a feedstock. Even with a pre-treatment step to remove sulfur, the susceptibility of dewaxing catalysts to sulfur or nitrogen poisoning limits the types of basestocks that can be processed by catalytic dewaxing. Additionally, if a reactor “upset” occurs, so that feedstock is not processed properly in the pre-treatment step, it may be necessary to replace a dewaxing catalyst exposed to high levels of sulfur or nitrogen.
An alternative for feedstocks containing higher levels of nitrogen and sulfur is to solvent dewax the feedstock. While solvent dewaxing is effective for feedstocks with higher levels of impurities, solvent dewaxing is much more costly than catalytic dewaxing. Thus, a catalytic dewaxing solution for dewaxing of high impurity level feedstocks would be preferred.